This invention relates to an electron beam apparatus and more particularly to an electron beam apparatus suitable for accurately measuring characteristics of semiconductor circuits, formed on a wafer, by using an electron beam tester.
The electron beam tester has been used to inspect semiconductor devices formed on a wafer and for the inspection, as discussed in Japan Society for the Promotion of Science, Application of Charged Particle Beam to Industry No. 132 Committee, No. 97 Research Conference Reports, pp. 108-111. The wafer is placed within a specimen chamber and semiconductor circuits on the wafer are operated under the application of voltage fed through a probe card which is brought into contact with the wafer. Encountered in this measurement, however, is a problem-that a probe of the probe card is held on one of bonding pads surrounding a semiconductor circuit in substantially vertical relationship to the one bonding pad and consequently a horizontal electric field generated from the probe tends to disturb loci of secondary electrons in the vicinity of the probe.
More particularly, as diagramatically shown in FIG. 2, a probe 3 affects secondary electrons. The probe 3 is held in contact with a pad 4 formed on a silicon substrate 6. In the electron beam tester, an electron beam 1 is irradiated or bombarded on one of wiring conductors formed on the silicon substrate 6, for example, a conductor 5 and energy of secondary electrons 2 emitted or excited from a bombarded portion is analyzed to measure electrical potential at the conductor 5. The manner of analyzing energy of the secondary electrons is detailed in JP-A-60-6876 and will not be described herein.
The measurement is however affected adversely by the probe 3 when conducted under the application of a voltage of, for example, 5V through the probe. Since mean energy of the secondary electrons 2 is as low as about 2 eV, the secondary electrons are drawn along a horizontal (more generally, transverse) electric field generated from the probe 3 and can not be detected by means of a detector (not shown) disposed upwardly of the probe card. Presumably, this adverse influence may be avoided by applying a vertical (more generally, longitudinal) electric field which can overcome the horizontal electric field due to the probe 3 but practically the application of the intensive vertical electric field sufficient to overcome the horizontal electric field is difficult to achieve near the probe.